Mientien tree frogs in the city of Taipei woo females from storm drains.

The frogs seem to be using city drains to amplify their voice to attract females.

"Calls emitted from inside the drains were louder and longer than those outside - both important mate-selection criteria for choosy females in many frog species," said lead researcher Yu-Teh Kirk Lin from National Taiwan University in Taipei.

Although impossible to distinguish with the human ear, acoustic analysis software revealed the drain calls to be about four decibels louder than those outside, he added.

"The lengths of all 13 notes in a frog’s call were also 10 percent longer when the call was emitted from inside the drains," he stated.

This is perhaps the first study to show that an animal preferentially uses human-made structures to enhance its amorous sounds.

"These males could be taking advantage of the enhanced acoustics in drainage ditches to outdo their competition," researchers said.